1. Field of the Invention
The present invention generally relates to methods and systems for detecting defects on a reticle. Certain embodiments relate to a method for detecting crystal growth defects on a single die reticle.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
The terms “reticle” and “mask” are used interchangeably herein. A reticle generally includes a transparent substrate such as glass, borosilicate glass, and fused silica having patterned regions of opaque material formed thereon. The opaque regions may be replaced by regions etched into the transparent substrate. Many different types of reticles are known in the art, and the term reticle as used herein is intended to encompass all types of reticles.
A process for manufacturing a reticle is in many ways similar to a wafer patterning process. For example, generally, the goal of reticle manufacturing is forming a pattern on a substrate. In this manner, reticle manufacturing may include a number of different steps such as pattern generation, which may include exposing a substrate having a resist layer formed thereon to a light source in a predetermined pattern. Alternatively, reticles may be patterned by e-beam direct write exposure. After the exposure steps, the reticle is processed through development, inspection, etch, strip, and inspection steps to complete the pattern transfer process. Defects in reticles are a source of yield reduction in integrated circuit (IC) manufacturing. Therefore, inspection of a reticle is a critical step in reticle manufacturing processes.
Once a reticle is fabricated and inspected, it may be qualified as acceptable for manufacturing and released to manufacturing. During the normal course of the life of a reticle, however, defects can be introduced into the reticle. For example, after some exposures using reticles, particularly with deep ultraviolet (DUV) light, defects can appear on the reticles that can be traced back to crystalline defects growing on previously defect free reticle surfaces including those reticle surfaces that are protected by a pellicle. Such crystalline defects are also commonly referred to as “haze defects” or “reticle haze” because areas of the reticle containing such defects appear hazy. Reticle haze may occur when a cloudy substance forms as a result of airborne molecular contaminants reacting with moisture in the environment of the reticle. For example, it is possible that haze may be formed on reticles due to cleaning procedures conducted during the reticle manufacturing process. In addition, or alternatively, haze may be caused by the presence and concentration of airborne molecular contaminants in the manufacturing fabrication facility in which the reticle is being used. Regardless of the cause of reticle haze, the cost of haze defects on reticles can be exorbitant (e.g., in the millions of dollars) and is particularly problematic in fabrication facilities with DUV lithography tools. Accordingly, many manufacturers periodically image or otherwise test reticles to ensure that they are not defective.
The type of inspection, whether for qualification or re-qualification purposes, that can be performed for a reticle varies depending on the reticle itself. For example, some reticles include only a single die, while other reticles include more than one identical die. In instances in which a reticle includes more than one identical die, images or other output generated by an inspection system for one die can be compared to images or the other output for another die on the same reticle. Such “die-to-die” inspection is substantially effective, efficient, and inexpensive. Obviously however, such “die-to-die” inspection cannot be performed for a reticle that has only one die. In contrast, one common inspection method for detecting defects on a single die reticle involves using a reticle inspection system (such as one of those that are commercially available from KLA-Tencor, San Jose, Calif.) to inspect the reticle directly (e.g., by comparing light transmitted by the reticle to light reflected by the reticle on a location-by-location basis). However, although such reticle inspection systems are effective and have achieved great success commercially, such reticle inspection systems do have some disadvantages for some applications in that the reticle inspection systems have relatively high cost of ownership and relatively slow throughput.
Accordingly, it would be advantageous to develop methods and systems for detecting defects on a reticle, and particularly a single die reticle, that are effective, efficient, and inexpensive and are particularly suitable for applications such as reticle re-qualification for which there is typically little or no reticle inspection system availability.